There are systems that involve a tracking function performed by a centralized and stationary unit. Examples of such systems are shown in U.S. Pat. Nos. 5,594,425; 5,312,618; and 5,043,736. In the usual case, a target's location information is transmitted to a monitoring station where the information is processed and actions taken accordingly. A variation to this is shown in U.S. Pat. No. 5,389,934 which allows the searcher/controller to be mobile; where in one embodiment the system described is a rover which when called by a telephone would become active, relay a voice description of its location and then become inactive; and another embodiment provides an arrow visual to point in the direction of the target, but does not take advantage of the specific spatial relationship calculations used in the present invention.
Currently there is under consideration and implementation a concept referred to as E911 which contemplates that a cell phone user can make a “911” emergency call and a system will exist with a location technology that will enable locating the cell phone without any need to have the user interact. The location technology, the cell phone network and the cell phone (sometimes referred to as a handset) will enable the cell phone's location to be determined and communicated to a responding emergency service.
Numerous location technologies and standards are presently under consideration and implementation in conjunction with wireless networks in general and cellular networks in particular not only for implementation of the E911 capability, but for other purposes as well.
Many papers, announcements and reports describe these location technologies, how they function with wireless networks, in particular cellular networks, their pros and cons, and the ways in which they can provide useful services. A simple Internet search will suffice to find many such publications. Some of them are:
“Geolocation and Assisted-GPS”, Goran M. Djuknic and Robert E. Richton, a white paper published by Lucent Technologies-this document has a particularly helpful description of the various geolocation technologies;
“Location Technologies for GSM, GPRS and UTMS Networks”, a White Paper by SnapTrack, A QUALCOMM Company;
“Geolocation and Assisted-GPS”, by Djuknic and Richton, Bell Laboratories, Lucent Technology published in Computer magazine, February 2001;
“Assisted GPS: A Low-Infrastructure Approach”, by LaMance, DeSalas and Jarvinen, in GPSWorld, Mar. 1, 2002;
“An Introduction to SnapTrack Server-Aided GPS Technology”, by Mark Moeglin and Harvey Krasner, published on Aug. 10, 2001 as a White Paper;
“Satellite-Based Positioning Techniques”, by Jari Syrjarinne, published by Nokia.
“Hybrid Wireless Assisted GPS Architecture” a publication by SnapTrack;
“A Position Determination Service Standard for Analog Systems” published by TIA/EIA, Jun. 6, 2000 (see also TIA/EIA-553-A);
“Position Determination Service Standard for Dual Mode Spread Spectrum Systems” publication of TIA as standard 3GPP2 C.S0022-0-1;
“High performance wireless location technology” a news release by TruePosition, Inc.;
“LOCATION TECHNOLOGIES FOR ITS EMERGENCY NOTIFICATION AND E911”, By Robert L. French and Clement J. Driscoll a paper prepared for ION National Technical Meeting, Santa Monica Calif., Jan. 22-24, 1996. The content of all of these references is incorporated by reference into this specification.
Also an Internet search for the relevant standards bodies such as TIA's 3GPP (principally dealing with GSM networks) and 3GPP2 (dealing with CDMA networks) will provide information about the process of evolving technical standards. With such helpful descriptive material available it will not be necessary to provide exhaustive descriptions except to the extent necessary to understand the configurations of systems and operation of methods of the present invention.
Some of the location technologies are; Assisted GPS (AGPS), network wireless triangulation using Time Difference of Arrival (TDOA), Advanced Forward Link Trilateration (AFLT), Enhanced Observed Time Difference (EOTD), and/or Angle of Arrival (AOA) as well as hybrid solutions such as AGPS augmented with other location technologies that make use of all available measurements be they satellite or land based signals. For the purposes of this specification and claims the phrase: “land based location technology” will be used to define any location technology that makes use of measurements obtained from land based transmitters to form a position solution; such as: AFLT, TDOA, EOTD, AOA, or UTDOA. Also except if the context clearly indicates otherwise the words “position” and “location” are used interchangeably and are considered synonymous.